Slamming Genzyme Corp.'s use of non-union janitors, about a dozen union representatives protested Thursday outside one of the company's New York Avenue plants.

But, a Genzyme Corp. spokesman said the new company was hired because it provides better service in the "sterile clean rooms" at its New York Avenue facility.

"We require precise maintenance of sterile clean rooms," said Genzyme spokesman Bo Piela. "It is a highly complex, tightly regulated cleaning procedure performed by highly trained personnel. We felt the vendor was in the best position to provide us these very specialized cleaning services that are required in the state of the art facilities."

But, Adriana Fieldman, field director of Service Employees International 32BJ, said Genzyme got rid of the previous workers, who worked for a contracting service, because they were unionized. The company instead hired non-union Advanced Cleanroom Microclean, and about 60 people lost their jobs due to the change, she said.

"The problem is they did not offer any of the employees positions," said Fieldman. "They lost their jobs."

The dozen or so protesters stood in front of Genzyme, walking back and forth holding signs while one man yelled into a megaphone. None of those participating in the protest were current or former employees.

Members of the union still work at a majority of Genzyme facilities, including Framingham, performing cleaning services, Piela said.

However, Fieldman is worried those jobs are in danger.

"We are concerned that this company will take over all of our jobs," she said.